Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: chrischris on April 26, 2016, 08:15:01 am

Title: Blues Junior transformer
Post by: chrischris on April 26, 2016, 08:15:01 am: Hi all,

Does anyone have any hookup diagrams for the Export PT (P/N 49968)? Need to hook it up for 240V UK.

I've tried to piece it together by looking at the original BJr Schematic but don't get it.

Cheers,

Chris.
Title: Re: Blues Junior transformer
Post by: chrischris on April 26, 2016, 11:09:09 am: Just to elaborate a little on my confusion, the US model has 1 primary with 2 wires, the export model has 7 wires on the primary side and what looks like 4/5 primaries that you can swap around to the different "P" points on the board to get the different voltages required for 100V, 230V, 240V.

I just need to know what to put where on this Hoffman build, anyone got any ideas?
Title: Re: Blues Junior transformer
Post by: EL34 on April 26, 2016, 02:42:33 pm: Give the guys links to the schematic so they have something to work with

Chris has already looked at this post
http://el34world.com/Forum/index.php?topic=18687.0 (http://el34world.com/Forum/index.php?topic=18687.0)
Title: Re: Blues Junior transformer
Post by: chrischris on April 26, 2016, 05:30:23 pm: Cheers Doug,

Ok so I think I have figured it out now, a combination of the thread Doug mentions above (more specifically this diagram - http://el34world.com/Forum/index.php?action=dlattach;topic=18687.0;attach=51028;image (http://el34world.com/Forum/index.php?action=dlattach;topic=18687.0;attach=51028;image)) and the original Fender Schematic.

The post above is for 230V so knowing this I looked again at the Fender Schematic and think I have made sense of that now, but if anyone could check my logic and confirm then I'd very much appreciate it.

(http://s32.postimg.org/4ezmrn9vp/BJr_PT_240_V.png)

Basically I think I connect the Violet to P4 (fuse) and Black to S2B (switch) and join the Black/Green to the Black/Yellow, isolate the others then I think I'm in business.

Any thoughts or screams to the contrary? Looking at it now it seems so simple, but sometimes you need to go through the pain to learn the lesson I guess, and it's only easy once you know it...which now I hopefully do.

Cheers,

Chris.
Title: Re: Blues Junior transformer
Post by: HotBluePlates on April 27, 2016, 01:12:42 am: Simple question, but with big implications: Are you keeping the stock Blues Jr board, or are you replacing it? Is getting rid of the stock board why you're needing to ask about wiring the power transformer, as the board will no longer do it for you?
Title: Re: Blues Junior transformer
Post by: chrischris on April 27, 2016, 03:57:42 am: I'm using a Hoffman replacement P2P board, hence the confusion.

I'm fairly sure I understand it now, but just want to be sure.

Cheers.
Title: Re: Blues Junior transformer
Post by: HotBluePlates on April 28, 2016, 07:41:29 am: Quote from: chrischris on April 26, 2016, 05:30:23 pm
... Basically I think I connect the Violet to P4 (fuse) and Black to S2B (switch) and join the Black/Green to the Black/Yellow, isolate the others then I think I'm in business. ...

Sorry for the slow reply; I suspect you may have already just tried your plan and found it works.

Yes, you were correct in the wiring steps you noted.

At first I was thrown by the different connection designations between the different Blues Jr schematic versions, and the illegible text on one of them.
Title: Re: Blues Junior transformer
Post by: chrischris on April 28, 2016, 08:09:11 am: Yeah they're not the best quality, but I think the PT has remained constant through the versions, just the Pin designations have changed I think.

Thanks for the confirmation, I actually haven't got that far yet, wiring up the tube board today, then pots, then at the weekend I should be ready to start powering it up. Exciting stuff! :)

Cheers for the help! :)